1. Field of the Invention
The present invention relates to an apparatus and method for transmitting and receiving control information for uplink data in a mobile communication system and a system thereof. More particularly, the present invention relates to an apparatus and method for transmitting and receiving control information for uplink data considering a change in buffer status of a User Equipment (UE), and a system thereof.
2. Description of the Related Art
In the 3rd Generation Partnership Project (3GPP), standardization for Long Term Evolution (LTE) as one of the next-generation mobile communication systems is under way. LTE is a technology for implementing high-speed packet-based mobile communication having a data rate of a maximum of 100 Mbps, aiming at deployment in around 2010. For example, this includes a high-speed wireless access technology and a Multi Band Multi Carrier (MBMC) technology. Based on a 20 MHz bandwidth, the technology is expected to offer services supporting data rates of 100 Mbps in the downlink and 50 Mbps in the uplink. In conclusion, it will provide a smooth transition path to the 4th Generation (4G) system.
As a configuration of the currently proposed LTE, a 2-tier model has been proposed, which is composed of an Enhanced Node B (ENB) serving as a Node B and a Radio Network Controller (RNC), and an Access Core Gateway (ACGW) serving as a Serving GPRS Support Node (SGSN) and a Gateway GPRS Support Node (GGSN). Such an LTE configuration is composed of an ENB that performs an Automatic Repeat reQuest (ARQ) function, or retransmission technology, and a Radio Resource Control (RRC) function, or a function for determining wireless resources and handover, and of an ACGW that serves as a core network in LTE. The GGSN, SGSN and RNC nodes are implemented as a single central node of ACGW. Therefore, the ENB has been designed in a flexible structure where it can be connected to several LTE ACGWs, like the lu interface in UMTS Terrestrial Radio Access Network (UTRAN).
In LTE, all user traffic, including real-time services such as Voice over Internet Protocol (VoIP), will be serviced over a shared channel, and thus there is a need for an apparatus for gathering state information of UEs and performing scheduling depending the state information. The scheduling is performed by a scheduler of an ENB, and the scheduler manages and allocates wireless transmission resources, and receives buffer status reports from UEs before allocating uplink wireless transmission resources.
When a UE is driving several services, radio bearers are formed separately for the services in the UE, and a buffer is provided for each of the formed radio bearers. The UE reports to the ENB the amount of data separately stored in buffers for the radio bearers, or sums the amount of data stored in each radio bearer group made by grouping radio bearers having similar properties, and reports the results to the ENB. Herein, control information including buffer status for each radio bearer or each radio bearer group is referred to as ‘scheduling information’.
The ENB performs scheduling depending on the buffer status reported by UEs, and in this case, the date with the highest priority that the UE transmits to the ENB greatly affects the scheduling. The priority of transmission data is assigned to each radio bearer independently, and may be implemented as an index indicating an importance of the data transmitted over the radio bearer. For example, a higher priority is assigned to transmission data on a radio bearer for transmitting/receiving control messages, while a lower priority is appointed to transmission data on a radio bearer over which a packet service, which is insusceptible to delay, is provided. The UE and the ENB commonly perform scheduling using priority as an absolute criterion. With reference to FIG. 1, a description will now be made of a process of performing scheduling using priority as an absolute criterion.
FIG. 1 is a diagram illustrating a procedure for reporting by a UE the highest priority of transmission data to an ENB in a conventional mobile communication system.
In describing the procedure illustrated in FIG. 1, it will be assumed that capacities of transmission data with priorities 1˜4 are 200 bytes, 200 bytes, 300 bytes and 240 bytes, respectively. Although the capacities of transmission data are limited to particular figures in the description of FIG. 1, this is not intended to limit the scope of the present invention. In addition, the Node B referred to herein has a substantially similar meaning as the ENB.
Referring to FIG. 1, if the transmission of data occurs in step 101, a UE 10 sends a request for an allocation of transmission resources to an ENB 20 in step 151. Upon receipt of the transmission resource allocation request, the ENB 20 allocates, in step 153, transmission resources with which it can transmit 300-byte data to the UE 10. Upon receiving the allocated transmission resources over which the 300-byte data can be transmitted, the UE 10 includes, in a Medium Access Control Protocol Data Unit (MAC PDU), 200-byte data with priority 1 corresponding to the highest priority among the priorities of transmission data, in step 103. In this case, the UE 10 allocates the remaining 100-byte transmission capacity in the 300-byte transmission capacity to data with priority 2, or the next priority, and includes 100 bytes in the priority-2 data in a MAC PDU. After allocating all the 300-byte transmission capacity allocated from the ENB 20 according to priorities of the transmission data. In this manner, the UE 10 transmits to the ENB 20 a MAC PDU composed of the priority-1 data and the priority-2 data in step 155.
Upon receipt of the MAC PDU, the ENB 20 considers, in step 131, the lowest priority among the priorities of data contained in the MAC PDU as the highest priority of data that the UE 10 currently stores. That is, the ENB 20 determines priority 2, or the lowest priority among the priorities of data contained in the MAC PDU, as the highest priority among the priorities of data that the UE 10 currently stores. In step 133, the ENB 20 generates scheduling information considering the determined highest priority and transmits the scheduling information to the UE 10.
The transmission resources that the ENB allocated to the UE are preferentially distributed to the highest-priority data. Thus, if the highest-priority data that the UE should transmit is continuously generated before sufficient transmission resources are allocated to the UE, no lower-priority data may be transmitted to the ENB. In this case, for guaranteeing minimum transmission of lower-priority data, i.e., for starvation avoidance, it is possible to guarantee the minimum data rate for the lower-priority data. A description will now be made of a procedure for guaranteeing the minimum data rate of the lower-priority data.
If the ENB 20 allocates 50-byte transmission resources in step 157, the UE 10, which is allocated the transmission resources, determines in step 105 whether there is a need to guarantee the minimum data rate for priority-4 data. If so, the UE 10 preferentially allocates, in step 107, transmission capacity to the priority-4 data that needs the guarantee of the minimum data rate, regardless of a priority of other data. That is, the UE 10 includes 50 bytes in the 240-byte transmission capacity having priority 4 in a MAC PDU and transmits the MAC PDU. Upon receiving the MAC PDU containing the priority-4 data in step 159, the ENB 20 determines the priority 4 among the priorities of the data contained in the received MAC PDU as the highest priority of transmission data of the UE 10 in step 135. In step 137, the ENB 20 generates scheduling information considering the determined highest priority, or priority 4, and transmits the scheduling information to the UE 10 in step 161.
However, although the actual highest priority of data that the UE should transmit at the time the MAC PDU is transmitted to the ENB is priority 2, the lowest priority among the priorities of the data contained in the MAC PDU is priority 4. In other words, if the ENB determines the highest priority based on the lowest priority of the received MAC PDU, it may misjudge the highest priority of data that the UE should transmit. Therefore, the ENB cannot correctly determine the actual highest priority of the UE's transmission data, thereby causing an inefficient allocation of transmission resources.